It is generally recognized that steam and hot water radiators cannot efficiently transfer heat through the radiator walls if air is present in the heating medium. Numerous types of vent valves have been used with prior art steam and hot water radiators. Some of these valves rely on floating or thermally expansible elements to control venting of air. The pior art vent valves have been generally complex in construction and, hence, relatively expensive. Also, it is applicant's belief that existing vent valves have been designed specifically for use with continuously fired furnaces such as coal burning furnaces, wherein pressure within the radiators reached two or more p.s.i.g. Applicant has found that some prior art vent valves are not suitable for use with intermittently fired steam and hot water heating systems wherein lower pressures in the order of one p.s.i.g. occur; for example air locks may develop and the radiator may fail to develop any appreciable heat because the air locks inhibits the flow of heating medium from the furnace to the radiator.
A number of prior art valves are disclosed the U.S. Pat. Nos. 1,275,750; 1,778,612; 2,287,075 and 2,340,220.